The invention concerns an apparatus for producing bituminous coated products from aggregates, bitumen and solid materials which can undergo deterioration if they are exposed to a high-temperature environmemnt.
In methods of preparing hot coated bituminous products in which aggregates without bituminous material and bituminous products are introduced into a drum rotatable about its longitudinal axis, the products containing bitumen must be introduced into the drum in a zone protected from direct contact with the flame of the burner, which generally enters at the inlet end of the drum, so as to prevent degradation of these bituminous materials under the action of an atmosphere at too high a temperature.
Thus, French Pat. No. 2,327,048, filed 8th Oct., 1975, by Creusot-Loire, recommends introducing liquid bitumen for incorporation with aggregates which have been dried in the drum, in a zone of the drum protected from the flame of the burner by a continuous opaque curtain constituted by the aggregates falling over the whole section of the drum during drying.
To form this curtain of material while allowing the flame of the burner to develop up to the drying zone, a set of specially shaped lifting devices is provided on the surface of the drum in this zone, allowing the curtain of material to form progressively in the drying zone while leaving a central space free for the flame to develop.
Such an apparatus also has the advantage of preventing aggregates introduced into the drum from falling back into the flame, thereby the formation of dust from the break up of these aggregates under the action of the heat of the flame.
Such an apparatus, however, is unsuitable for solid materials containing bitumen, such as recovered bituminous products, or any other solid material subject to deterioration in a high-temperature environment, which must be introduced into the drum.
Such solid materials may be, for example, rubberized compounds, plastic materials, sulfur, coloring products such as a metal oxide or bitumen in flakes.
Even if such materials do not fall into the flame of the burner, they can be destroyed by the heat of the flame unless they are protected from its radiation in the introduction zone and the drying zone of the drum.
There are other known apparatuses for producing bituminous coated products from fresh aggregates, bitumen and a certain proportion of recycled coated products in which the recycled coated products are introduced into the drum in an intermediate zone between the inlet end through which the fresh aggregates enter and the outlet end of the drum through which the coated products are removed. Such apparatuses use the principle of forming a curtain with the fresh aggregates introduced into the drum, the recycled aggregates being introduced into a zone of the drum which is protected from the flame by this curtain of material.
The recycled materials are introduced into the drum through openings provided in the wall of the drum, and mechanical devices, such as hatches closing by gravity, prevent the material leaving the drum at this intermediate zone for introducing recycled materials.
Such apparatuses have some disadvantages, since the fresh aggregates introduced through the inlet end of the drum fall into the spatial zone in which the flame develops, and as a result cause the formation of dusts which are conveyed by the gases coming from the burner and passing through the drum. In practice, in these apparatuses, the region for drying the fresh aggregates has lifting devices which cause the fresh aggregates to fall over the whole section of the drum, especially into the flame of the burner.
This allows the intermediate zone into which the recycled materials are introduced to be protected from the flame of the burner, but interferes with the development of this flame and causes the formation of dusts which are found in the gas expelled into the atmosphere.
These apparatuses also need mechanical members such as hatches which are movable with respect to the casing of the drum at the intermediate zone for introducing recycled materials. The conditions in which the drum works makes the use of such movable closure devices undesirable.